~> (cube, int) operator was especially designed for knn-gist search.
However, it appears that knn-gist search can't work correctly with current
behavior of this operator when dataset contains cubes of variable
dimensionality. In this case, the same value of second operator argument
can point to different dimension depending on dimensionality of particular cube.
Such behavior is incompatible with gist indexing of cubes, and knn-gist doesn't
work correctly for it.
This patch changes behavior of ~> (cube, int) operator by introducing dimension
numbering where value of second argument unambiguously identifies number of
dimension. With new behavior, this operator can be correctly supported by
knn-gist. Relevant changes to cube operator class are also included.
Backpatch to v9.6 where operator was introduced.
Since behavior of ~> (cube, int) operator is changed, depending entities
must be refreshed after upgrade. Such as, expression indexes using this
operator must be reindexed, materialized views must be rebuilt, stored
procedures and client code must be revised to correctly use new behavior.
That should be mentioned in release notes.
Noticed by: Tomas Vondra
Author: Alexander Korotkov
Reviewed by: Tomas Vondra, Andrey Borodin
Discussion: https://www.postgresql.org/message-id/flat/a9657f6a-b497-36ff-e56-482a2c7e3292@2ndquadrant.com
Commit 33bd250f6c could have done with
some more review:
Adjust coding so that compilers unfamiliar with elog/ereport don't complain
about uninitialized values.
Fix misuse of PG_GETARG_INT16 to retrieve arguments declared as "integer"
at the SQL level. (This was evidently copied from cube_ll_coord and
cube_ur_coord, but those were wrong too.)
Fix non-style-guide-conforming error messages.
Fix underparenthesized if statements, which pgindent would have made a
hash of, and remove some unnecessary parens elsewhere.
Run pgindent over new code.
Revise documentation: repeated accretion of more operators without any
rethinking of the text already there had left things in a bit of a mess.
Merge all the cube operators into one table and adjust surrounding text
appropriately.
David Rowley and Tom Lane
Introduce distance operators over cubes:
<#> taxicab distance
<-> euclidean distance
<=> chebyshev distance
Also add kNN support of those distances in GiST opclass.
Author: Stas Kelvich
Previous commit modified the test case, but I didn't update cube.out
expected output file in previous commit because it was not needed by the
platforms I have easy access to. Buildfarm animal 'dugong', running
"Debian 4.0 icc 10.1.011 ia64", has now gone red because of that, so update
it now.
Also adjust cube_3.out. According to git history, it was added to support
64-bit MinGW. There is no such animal in the buildfarm, so I'm doing this
blindly, but it was added quite recently so maybe someone still cares.
